Plates and Hoses on Top of Black Water Tank - 63 Motoryacht

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New to us 1986 63 Motoryacht. I have owned a Hatteras before, so fairly familiar with how systems in 80's were installed. Black water
tank has two plates.

1. On the left, in the picture, is a square plate secured with 12 machine screws. A rubber gasket about
1/4" thick protrudes around edges. 3 of the screws just spin and are likely corroded away. I am going
to pull and reseat. Are these machine screws threaded in to the fiberglas or a metal collar? This plate
has 2 GROCO labels and several wires that have been cut. Is this a liquid level sending unit?

2. On the right, in the picture, is a fiberglas plate that appears to have been poorly attached/repaired by a
PO. I plan to remove and re-glass. Both of these access plates are leaking air (small amount of bubble
and liquid), as if the tank is pressurized. I have cleared the vent line with freshwater and pressurized
air. Perhaps the tank is full(I am not able to verify, until next weekend, that the overboard pump is
actually removing fluid)?

3. Heads were replaced with Vacu-flush and each head (4) has its own hose attached to the black
water tank. So, I should have 4 inflow hoses, 1 vent hose and 1 pumpout hose. The pumpout hose
runs to a Y-valve that either can go to pumpout deck plate or a macerator pump leading to a below
water though-hull. This all male sense, but there are 7 hoses attached to the top of the black water tank,
not 6, as counted in prior sentence. The 7th is a direct hose upward toward the pumpout deck plate.
However, there is only 1 pumpout deck plate, so I can only guess that this is an old hose, prior to
the installation of the y-valve-macerator pump assembly. I cannot, at tis time, move to a pumpout station to
see which hose will evacauate fluid through the deck plate. Thoughts?

John McCarley
Water Colors
Wrightsville Beach NC