I will assume you mean an older H22 ('82-'85(6))... I have seem many postings were a bilge pump is placed in the cabin floor opening just under the sink/companion way step. Although this is easy access, it will still leave almost 3 gallons or so from that point to the lowest point, where the keel bolts are. How i know that its 3 gallons is another story. From there people have run bilge lines to the stern, or used the thru-hull for the sink. I have mine planned out, and will run the line to the stern.
I have heard (but no pics) of someone who installed a bilge about where the keel bolts are, by cutting out some of the wood flooring, and removing some of the let balast (not alot, just enough to fit a small Rule pump in), then run the bilge hose to starboard.
As I said if you install it under the step, you would have to run some sort of a line down to a lower point if you want all the water out. I am out of ideas on that.
Mine is an 85, and when I had a leak, I could easily pump 10 gallons of water out of it. Once over about the 12 gallon mark though it was pretty obvious there was a water problem. Before I hauled it out three weeks ago, I pumped about 40 gallons out of it. But the water was about 4 inches over the cabin floor.
If you are having that much water, you really need to find the source of the leak first then worry about the other things. I wasnt able to completely pump all the water out of my bilge either. The only way I got all the water out was when I had it hauled out and removed the keel bolts... but as i said thats another story (for which I have pictures for).