Weird holding tank!!! Or is it?

[Tomtom39]

Dear all,
Hope the season is going well for everyone?
I have been investigating bad smells associated with my holding tank and once I had removed my heads false wall to reveal my holding tank I have been surprised to find my holding tank which is unusual to what I am used to!
It does not have a gravity pipe from the bottom it seems to have two pipes coming from the side at the top. There is also a pump out hose on the top which is normal and a vent hose.
In short do some holding tanks always have stuff in it unless pump out at pump station! Or using a pump on board? Can someone shed light!
This yacht uses the one large holding tank for both heads so both pipes come from toilet waste and enter the holding tank
Any help would be great
Thanks
Nick

[sailorboy1]

On the 2 boats I've never had a fitting at the bottom of the tank.

My first boat didn't have any fitting on the bottom and the manual pump sucked off the deck pump out via valving (this fitting was on the top of the tank). The boat had a wye valve to pump directly outboard when allowed. This boat probaly could pump the tank to the same level as a pumpout boat etc could from the deck.

My current boat has a connection on the side of the tank at the bottom (it's on the side not the botton of the tank) for using the on board pumpout. It doesn't have a Wye valve and everything always goes to the holding tank. On this boat the on board pump doesn't get the last couple of inches in the tank as the pump starts drawing air first.

[Tomtom39]

Thanks for the response.
From what you say your first boat had to be pumped out by a marina when full unless you fitted a manual pump on the boat which would then do the same job and pump over the side when at sea?
Thanks nick

[sailorboy1]

Originally Posted by Tomtom39

Thanks for the response.
From what you say your first boat had to be pumped out by a marina when full unless you fitted a manual pump on the boat which would then do the same job and pump over the side when at sea?
Thanks nick

It had a manual pump on the boat. Head could line up to the holding tank or overboard. The tank could be pumped from a marina or with the on board pump. All that was needed was to line the valve correctly.

Lots of ways to deal with sh*t and I don't think mine was unusual.

[Dsanduril]

I don't think the arrangement you describe is uncommon. For a gravity drain to work the bottom of the holding tank has to be above the waterline, and most holding tanks end up getting buried much deeper than that (amongst other things, it's nice to keep the weight of a full tank low in the boat).

Depending on the room available, a few tanks may have the pump connection on the bottom, but it is usually an internal stinger from the top. So, the only exit is by suction from the pump out connection on deck. That can be the marina pump out or your own on-board pump. Either way there will usually be a "heel" of liquid in the tank that cannot be removed. To get the tank as clean as possible you have to rinse with water, pump, rinse, pump... Not ideal, but the way many installed tanks work.