<Mike wrote in part: Access to the tanks is very limited.? The tanks are iron or steel.? Any advice would be appreciated.> We just repaired one of our 475 gallon tanks which was leaking in 3 pinhole in the bottom. Our tanks are approximately 4 X 8 X 2. We cut 3 12" holes, one in each of the baffled sections in the side of the tank about 6" above the bottom. These holes we made for the SeaBuilt 14" access covers which we ordered from Seabuilt in Bellingham, Washington. These 12" holes allowed easy access to the inside floor of the tanks. We had sounded the bottom with a small flat hammer as found that the pinhole were at the bottom of craters. There were many small craters but 99% of them were very shallow. Only the ones leaking were deep. An intense cleaning of degreaser several times with a detergent and small brass wire brushes soon had the bottom very clean. A couple of wipe out with acetone and then alcohol had the bottom sparkling clean....well maybe not sparkling but clean. We applied a thinned coat of 100% solids no blush epoxy to the bare steel to making sure it flowed well into all the craters. Then a coat of slightly thickened with silica epoxy which filled the craters. This was followed by another coat thickened enough to flow well but coated the bottom of the tank perhaps a 1/16" or so. This was followed with two coats of Devoe epoxy tank liner. I ran all this epoxy, filler and paint 2/3" up the side to make sure the bottom seams were sealed too. Once it had all fully cured, about 7 days, we drilled the cover plate holes, bolted them on (they have inside and outside gaskets) and voila tank done and good for many years I suspect. I may have spent 30-40 hours on the work as it was work a bit and then leave it to dry etc...took 3 weeks from start to finish. BTW you either will need a positive air source to breath or a very good mask with the proper filter. Working with my head in the tank thru the 12" hole requires an up close and personal relationship with the tank. The solvents and the epoxy can be hazardous to your health. Also good ventilation keeps the flammables out of the boat. We have a positive air system in the engine room to keep the pressure up which lets the bad stuff or heat just be extracted. If the bottom of the tank is not wasted such that it likely to drop off I think opening a hole and doing what we did is a good method of getting more time out of the tanks for little money (I estimate we have less than a BU in the whole repair and most of that was for the access cover, shipping to Venezuela and customs duty (27%!). If the bottoms are wasted i.e. little sound metal left then this method won't work, IMO. We hope to change out our tanks to get more tankage but in case that doesn't happen I'm happy with this repair. As always YMMV..... Dave & Nancy Swan Song Roughwater 58