Why bother with an access hole under the base? I just replaced my old Jabsco with their latest model (all because the flange at the back of the
pump isn't sold anymore....the 24 year old toilet was fine otherwise!!)....and I just let the old bolts drop down in the base and used lag bolts into new holes I drilled (the old and new bases weren't the same spacing anyway).....if the first head lasted 24 years, I'm not going to have to do this again, and the lag bolts are holding the new head down just fine....I globbed a little 5200 into each hole too, just to give the lag bolt's threads a little help.