IP38 FW tank inspection port

We have an IP38 whose freshwater tank has never been cleaned. Although vacuuming through the small gauge access is commendable, it seems inadequate to fully clean the tank. We are considering installing a 6"-8" inspection plate in the tank, about 2' forward of the existing saloon access point. This would require cutting another access hole in the saloon sole. Has anyone performed this? Or does anyone know where the sole support frames are located? [We have already posed these questions to the IP factory]

Thank you, Hayden, for your insights.

We live aboard and cruise full time; and we drink our water, which does not smell. I have been boating since 1956, and the matter of tank cleaning is not one I feel is just confined to Island Packets. I have had a series of boats, the last prior one being a Krogen trawler. Cleaning tanks is well advised, both for fuel and water. We periodically have the fuel polished and the fuel tank cleaned; and we use a Baja filter when filling from questionable sources. We periodically put a gallon or two of white vinegar in our [empty] 40-gallon holding tank and let it sit a day or two before flushing it out (if you don't do this from time-to-time, the waste will settle into a gelatinous mass at the bottom of the tank).

We already pre-filter our fresh water with a carbon, not paper, filter at the time we fill our tank, thereby removing chlorine which we know is hostile to aluminum tanks. Furthermore, we also have a permanently-installed, whole-house, three-stage, 4 gallon-per-minute, filter system which includes an ultra-violet anti-biotic filter element and chamber to purify every drop that comes out. Lastly, being blessed with an abundance of caution and plenty of time, we have a PuR water filter element on the galley faucet (though the filter element at that point admittedly rarely needs changing).

As to flushing the lines, our fresh water system has a permanently-installed tee fitting with a pick-up tube, installed after the tank and before the pump. We use the tube to draw a solution of 1.5 cups of bleach (sodium hypochlorite)in 2.5 gallons of water into our lines from a 2 1/2 gallon water jug. We permit the solution to sit for an hour or two, then flush thoroughly with a full tank (157 gallons) of water.

All of which brings us to our first question. How does one best install an inspection port in a 157-gallon fresh water tank on an IP38? If you, or anyone, has drawings of the sole supports and/or tank, we would appreciate them. We have also posed our question to Warren Sweet and Karsten Johnson at IP.