Holding Tank Issues?

[Fly4hire]

Have a recently purchased 2002 Hunter 356 that appears to have the orginal holding tank in it. The tank has a significant concave shape on the sides, but there "appears" to be no venting issue and tank pressure appears equalized.

On Pump out the tank sucks in further but the vent is working as I can feel the suction at the vent but it does not keep up with the pumpout suction but this could be due to relative hose diameter of the vent vs pump out line (?)

I am concerned about the shape of the tank, and it does appear there was some very minor leakage at one point at the elbow fitting at the bottom of the tank. I can't tell if this is old or not or previously addressed.

There have been no odor issues provided I adequately flush the lav lines back to the tank on use.

Any suggestions for maintenance, preventative or otherwise welcome.

 

[kloudie1]

Vent is not large enough or it is partially plugged with something, a bug nest at the outlet is normal as well as pluggage where the tank vent fitting is on the tank.

 

[Peggie Hall HeadMistress]

Claude is right...

Vent is not allowing enough air into the tank to keep up with the pumpout suction.

The most common locations for a vent line blockage are the vent thru-hull and the connection to the tank--both the tank vent fitting and that end of the vent line. Start by removing the pumpout cap to relieve any pressure in the tank...then scrape out the vent thru-hull with a screwdriver blade or whatever works. If there's a screen in it, remove it...screens cause more problems than they solve. Then remove the vent line from the tank and scrape out the fitting and that end of the hose. Now you SHOULD have a clear vent line that SHOULD allow pumpout without risk of imploding the tank.

Ideally, a new 1" vent line should be installed...which isn't nearly as hard to do as it used to be, thanks to a li'l gadget called the UniSeal UNISEAL . This will also require a new 1" thru-hull--an open "bulkhead" or "mushroom" thru-hull that allows the vent line to be kept open by backflushing it every time you wash the boat and/or pump out. At the very least I'd replace the existing "vent" thru-hull that doesn't allow enough air to maintain the tank aerobically, even if it does allow enough to keep up with any extra-strong pumpout, with an open bulkhead fitting.

What's the tank made of? Is it permanently concave, or being sucked in by the pumpout? If you don't know, watch it during pumpout to see what's happening. As for the fitting that may or may not be leaking...it's easy to find out: wrap a rag around it for a while. If the rag stays clean and dry, it's not leaking...if it doesn't, it's gonna require a new tank I'm afraid...'cuz whatever caused the distortion that created a leak can't be reversed.

I'll be happy to help you do whatever needs to be done...meanwhile, there's a lot of good info in the discussions in this forum and you might also check out the link in my signature here.