These are some of the tools that I used to remove the lid from the tank.

The lid was leaking but the seal was very difficult to break. I cut around the entire perimeter of the tank with a razor knief. Then I inserted the putty kniefs under the lid to break the seal.

Assortment of tools used to lift the tank lid.

Once the caulking is cut with the razor, you will need to get something under the lid. I used several putty knives and a small pry bar to get the lid started.

You want to be careful so you do not damage the lid, so go slow.

You need to start somewhere.

Once the lid has been removed, it is time to remove all of the caulking and clean the inside of the tank.

I used the painters knief to scrape the old caulking. This takes a while and you want to be sure that you do not chip up the fiberglass too bad. It will make sealing the lid that much more difficult.

Ugly.

Be sure that you get all of the old caulking and mold off of the lip.

Get all of the old stuff off.

One of the real problems was that the old holes were oversized.

I filled these holes with Marine-tex and redrilled them for the new screws.

Oversized holes.

This is the outlet for the tank. It is in the lowest point in the tank.

Outlet

This is the new Butyl Rubber gasket. It is 1/8 strips that were cut to length and radiused at the corners to fit.

Before laying down the rubber, I put a double row of silicone caulking under the rubber.

New Butyl Rubber Seal

This is one of the corners. Just cut it to fit as close as possible.

Radius corners

This is the the tank with the baffle in place.

I am ready to lay down a double bead of caulking around the entire edge. One bead on the inside and one on the outside of the rubber gasket.

Almost ready to go.

I let the caulking sit for about 1 hours before placing the lid on the tank.

Then I placed the four corner screws in place and one screw in the middle of each side. I did NOT tighten these down. I just screwed it down enough to make good contact between the lid and the caulking.

The next day I finish replacing all of the screws and tighten everything down good. Then I caulked around the entire lid to finish it off.

I waited until the following week before filling it with water.

As of now everything looks good and hopefully I will not have to mess with it for several more years.

Finished product