Holding tank pressure relief valve

[brettportzer]

Revamping my sanitation system, using the fiberglass in keel tanks.

Knowing these tanks are sensitive, is a pressure relief valve recommended?

Here is an example of what I mean:

https://marinesan.com/tanksaver-relief-valve/

[SKYCHENEY]

As long as your vent line is clear, you should be all set.

[q240z]

At our yacht club, the pump-out system was so strong it would pull the water out of the toilet bowls then draw additional air through the empty bowls as it emptied the tank. The 5/8" vent hose was free-flowing, it just couldn't keep up with the draw from the pump.

These were new but conventional grinder-type marine toilets. If you have Vacuflush or some other fancy-schmancy system, they may not function like vent bypasses as the grinders do.

[tjshuler]

At our yacht club, the pump-out system was so strong it would pull the water out of the toilet bowls then draw additional air through the empty bowls as it emptied the tank. The 5/8" vent hose was free-flowing, it just couldn't keep up with the draw from the pump.

These were new but conventional grinder-type marine toilets. If you have Vacuflush or some other fancy-schmancy system, they may not function like vent bypasses as the grinders do.

Somewhere between this setup at your marina and nearly all other pump out stations I have experienced would be optimal.

[Captain Ralph]

So, pressure relief from pump out vacuum, not expanding gasses.

We had fresh rotocast plastic tanks in our boat 16 years ago, our marina at that time had pump out plumbing built into the docks.
With fresh vent hoses, the marinas pump out would draw the water then air thru the ole Crown heads and the new vent and draw the tanks inward into a scary shape.
On another boat, the discharge pumps duck bill valves were drawn backwards.

It was on a new Meridian when I first noticed that lil valve. That boat just took seconds for all to get pumped out.

If you are installing a new Type III tank and use deck pump out service, I do recommend it.

[rwaldrop13]

I actually just had an issue with this today, caused by my recent discovery that the tank hose from the V-berth head was cut off about 8 inches from the tank fitting and hanging into the starboard engine room bilge. I capped the hose, and then about a week later discovered my vent filter had clogged. I'm guessing that my vent hose was actually clogged before I capped that fitting, and pressure pushed matter into the filter. The v-berth head toilet had been "disconnected" long before we bought the boat, and we removed the toilet from that head. Well, here I am about 2 months later replacing the $150 vent filter again because I didn't take 2 simple steps - One, wash out the vent hose back to the tank before replacing the filter, and two, pump out while doing that to ensure the vent line was clear. I washed the line out today while the pumpout system was running, and could hear the water sloshing into the tank and then out thru the pumpout hose. Moral of the story is, keep your vent line clear. I'm adding a monthly vent line washout to my maintenance schedule.

[cww]

At our yacht club, the pump-out system was so strong it would pull the water out of the toilet bowls then draw additional air through the empty bowls as it emptied the tank. The 5/8" vent hose was free-flowing, it just couldn't keep up with the draw from the pump.

These were new but conventional grinder-type marine toilets. If you have Vacuflush or some other fancy-schmancy system, they may not function like vent bypasses as the grinders do.

I wish my marina's pump was like that. Ours is slow as hell, and you end up sitting there for 30+ minutes holding that thing in 100 degree hear with the florida sun beating down on you. Most of them are like that wherever you go.

[Fanfare]

On our leisurely return from Key West in April every marina I telephoned told me their pump out station was broken. Not counting the one in Miami that told me theirs was working, and then after refueling admitted they did not have one at all. Had to get to Ft. Lauderdale to pump out before storage. In such a situation you can guess what most boats must do. Bummer!

[rwaldrop13]

Now I have a new mystery. This morning my heads acted like tank was full again. I checked vent filter and there was a little moisture in the tank side. I left vent filter off and pumped the tank, flushed the heads while pumping, all seemed normal. My thought is that there is still so much sludge even after 2 years of pumping on a regular basis, washing out and treating, that I need to try an aggressive approach. I was thinking wash hose down the vent line while pumping, and repeat on alternating days while treating tank at same time. Local vendor swears by Cascade dishwasher powder, since it's enzyme-based but inexpensive.

Anyone have a recommendation for chemically de-sludging the tank? Experience with Rid-X or a similar product?

[firbanks]

Haven’t used Rid-X but there are lots of ways to attack this. Early days of ownership we tried Odorlos which was decent but not a top combo of impact and cost because it required more ongoing use and we have a big holding tank (=more chemicals). Camco makes a solution marketed to RVs that seemed inexpensive but was similar - good but not great. I found the biggest impact to truly de-sludge the tank was Zaal (brand) Noflex Digestor (product name). Key is each of these products works through a different mechanism but adding an oxidizer (Noflex) had biggest impact. Pump out. Add a few gallons of fresh water to cover bottom of tank. Add Noflex mixed with water in a milk jug (don’t be shy with powder) and dump down the pumpout deck fitting. Add more water to the tank (not more than 1/4 full maybe) from the pumpout fitting then pump out again in a few hours. Repeat if needed. After we de-sludged it made a huge difference - we’ve used noflex flushed down heads occasionally (after de-sludging) and haven’t had any trouble since (3-4 years in south Fla). Def keep that vent line clean. Noflex can be found at fisheries supply and marinesan among others. Public safety announcement - I wouldn’t mix these or other chemicals in the same cycle - only do one type at a time without flushing in between. Good luck!