Holding Tank Vent Configuration

[PhilPB]

Still tearing apart the boat and collecting last of the parts for the new water system with new water tank coming today.

The current configuration of the holding tank vent looks to be a bit kludged. The 1/2 barb outlet has an adapter on it, which looks to be 5/8 and it's connected using about 1" of clear water line and then transitions to 5/8" white hose that eventually weaves its way to a large pvc vent filter and ends up to an external vent.

I am changing out all hoses to and from the tank. I'm thinking that I should change the current vent configuration. The tank is under the galley floor, the floor has been partially opened up and accessible as I needed to explore the configuration. The tank is not original and looks in good shape (not discolored or out of shape).

The tank is in the middle of the boat and tends to get sloshed around as we are a relatively light boat and get knocked around a bit when we go out as there are lots of larger boats, blowing humongous wakes in our area and don't care how close they are to other boaters. Another topic for another day.

Anyways....

The questions currently are:
- If I increase the vent size, using a Uniseal fitting, can I vent directly from the top of the tank to a 90 degree pvc 3/4"-1" fitting on top? I would only have clearance for that type and size of fitting on top.
If yes, how long should the pipe protrude into the tank?
Should it be a straight fitting?

- Do I need an inline activated charcoal filter?

- Also, since I opened up the floor and are running all new Pex water lines, can they be run across the top of the holding tank? I do plan to have then wrapped in pipe insulation so there is no vibration or rubbing.

 

[rslifkin]

Skip the filter. And make the vent line as large as practical (preferably at least 1"). Also try to keep the run as short and straight as possible (tight bends restrict flow).

 

[PhilPB]

Skip the filter. And make the vent line as large as practical (preferably at least 1"). Also try to keep the run as short and straight as possible (tight bends restrict flow).

Can the vent outlet be placed on the top of the tank instead of the top of the side?

 

[rslifkin]

Can the vent outlet be placed on the top of the tank instead of the top of the side?

Yes, on top of the tank is no problem. My tank is configured with all top-mounted fittings (vent, inlet, and dip tube for pumpout).

 

[PM]

When Peggy reads this and responds, LISTEN to her.

A thumbnail guess at her response is this: get rid of the filters, ventilate the tank to both sides of the boat using as large a hose as convenient but at least 1 inch.

pete

 

[Bacchus]

All good advice. Make sure there are no low spots in the vent hose so you can back flush with a hose from outside periodically.

 

[PhilPB]

Also wondering if I could go with rigid pvc, as far as possible for the vent line to keep out low spots. The tank is secured and does not move.

 

[Comodave]

Can you get a vent to each side of the boat? That is the best configuration since it will allow air to flow through the tank no matter which way the wind is blowing. I put in 2 1.5” vents in our boat. Go as big a vent as possible. Air in the tank means that you will get aerobic bacteria, not anaerobic bacteria. Aerobic bacteria doesn’t smell bad, anaerobic bacteria does stink badly. Yes absolutely skip the filter it just will block air flow. Yes you can use PVC pipe. With the Uniseal you do need to extend the PVC pipe a couple of inches into the tank. I have put Uniseal in several boats.

 

[PhilPB]

The tank is 10" high. Taking that into consideration, would it be a problem having a vent tube protruding a couple inches into the tank?

 

[Comodave]

You will loose a bit of capacity. I recently put a Uniseal into my holding tank. Then I wanted to modify it and tried to pull the PVC out of the Uniseal and couldn’t get it to pull out, so it seems pretty secure.

 

[PhilPB]

You will loose a bit of capacity. I recently put a Uniseal into my holding tank. Then I wanted to modify it and tried to pull the PVC out of the Uniseal and couldn’t get it to pull out, so it seems pretty secure.

I guess that would probably be fine since the 1.5" input line is side mounted towards the top so I already need to take a couple inches from the top when we're talking capacity

 

[rslifkin]

I wouldn't want to let it stick into the tank any further than absolutely necessary. As soon as the tank level hits the bottom of the vent tube, the tank is full and you'll push waste out the vent if you try to add any more to the tank.

 

[PhilPB]

Dave, we're you nervous while drilling 2.5" in the top of
your tank?

 

[Comodave]

Dave, we're you nervous while drilling 2.5" in the top of
your tank?

No, I have put Uniseals in 4 boats and never had any problems. Just measure a couple of times and make sure you are drilling in the right place…. Carefully pull the hole saw out of the hole so you don’t drop the cut piece into the tank. When I cut the holes it never came off the hole saw, but just be careful.

 

[PhilPB]

I wouldn't want to let it stick into the tank any further than absolutely necessary. As soon as the tank level hits the bottom of the vent tube, the tank is full and you'll push waste out the vent if you try to add any more to the tank.

I just.looked again at the Uniseal site and they say to clear the inside of the seal by about an inch

 

[HeadMistress]

I've read the whole thread so far...You've gotten some good advice and some not so good. I have a few questions that need answers before I can offer any but I won't have time until about 3 pm CST this afternoon.


--Peggie

 

[PhilPB]

Thank you Peggie!!

 

[PhilPB]

Water tank was just delivered. Only thing left to get the requirements for, and then purchase is the vent line and associated fittings.

So far, we have:
Saniflex hose
Pex a pipe
Milwaukee Pex expander
Lots of ProPEX Tee's, Elbows, faucet adapters, rings, adapters, couplings, etc
Faucet, Shower
Hot water heater
Water tank
And the famous Raritan ME !

Time for me to get to work!

 

[Comodave]

Nice pile of equipment!

 

[HeadMistress]

Ok, I'm back, a bit later than I meant to be but life sometimes sets its own priorities.

Questions:

You said the tank is only 10" high...how many gallons? If you don't know, measure LxWxH in inches and divide by 231 (cu. in in a gallon). However, because those are outside dimensions and also because not every cubic inch of space is useable space, you need to multipy that by .9 to arrive at the approximate useable size. Then we can explore the size you'll need for your expected use of the boat.

Where is the head located in the boat? How far from the tank (in feet)? Forward or aft of the tank?

How long is the tank vent line? How straight? How high above the tank is the vent thru-hull? How much vertical rise?

That's enough information to give me a good start on what I need to know to give you good suggestions and advice.

-Peggie

 

[PhilPB]

Ok, I'm back, a bit later than I meant to be but life sometimes sets its own priorities.

Questions:

You said the tank is only 10" high...how many gallons? If you don't know, measure LxWxH in inches and divide by 231 (cu. in in a gallon). However, because those are outside dimensions and also because not every cubic inch of space is useable space, you need to multipy that by .9 to arrive at the approximate useable size. Then we can explore the size you'll need for your expected use of the boat.

Where is the head located in the boat? How far from the tank (in feet)? Forward or aft of the tank?

How long is the tank vent line? How straight? How high above the tank is the vent thru-hull? How much vertical rise?

That's enough information to give me a good start on what I need to know to give you good suggestions and advice.

-Peggie

Tank is ~ 21.75 gal (29"L x 9.75"H x 19.75"W)

Head is located middle of boat
Head is located starboard of tank, 1' ft. as a spider crawls, 3' hose from tank to Head (after ME install should be 2' -ish run

Tank vent line is now 9'. Not very straight, thru hull is 5' rise. Vent is now located after on Tank, if I could locate it to the forward top of tank it could be a better run.

 

[PhilPB]

Ok, I'm back, a bit later than I meant to be but life sometimes sets its own priorities.

Questions:

You said the tank is only 10" high...how many gallons? If you don't know, measure LxWxH in inches and divide by 231 (cu. in in a gallon). However, because those are outside dimensions and also because not every cubic inch of space is useable space, you need to multipy that by .9 to arrive at the approximate useable size. Then we can explore the size you'll need for your expected use of the boat.

Where is the head located in the boat? How far from the tank (in feet)? Forward or aft of the tank?

How long is the tank vent line? How straight? How high above the tank is the vent thru-hull? How much vertical rise?

That's enough information to give me a good start on what I need to know to give you good suggestions and advice.

-Peggie

Tank is ~ 21.75 gal (29"L x 9.75"H x 19.75"W)

Head is located middle of boat
Head is located starboard of tank, 1' ft. as a spider crawls, 3' hose from tank to Head (after ME install should be 2' -ish run

Tank vent line is now 9'. Not very straight, thru hull is 5' rise. Vent is now located after on Tank, if I could locate it to the forward top of tank it could be a better run.

 

[Bacchus]

You might consider running vent straight fwd under fwd bed area.
That was the only relatively EZ way I found to run my vent.
Benefit is air flow when moving and low probability of being blocked by other boats, docks etc. If there is any smell it's far from usual occupancy areas.
Only downside I find is inability to flush w have from outside.