All Hydro gear pumps have a plug at the top center inside of the body you can remove with an allen wrench that allows you to access the pump cavity for refilling (you fill it until fluid comes out the hole and replace the plug. Far as draining one with no filter, easiest way to drain it is remove the 2 hex screws that retain the pump housing on the front lower side of the motor and drain the fluid from that point. Just be sure to renew the 'O' ring and replace the cover exactly as it comes off (I mark the cover with a center punch so I can out it back on exactly the same way it comes off. If you put it on backwards (it will go one either way), it won't move as the pump isn't pushing any fluid. My wife's has no filters, mine does and I agree having the filters makes draining much easier but filling is through the plug up top.
I think Hydro Gear sells a refill kit with oil and a hose and fitting to go into the threaded port where the plug resides at. Not sure but I believe they do. Filters ain't cheap either. Just did mine a month ago and the filters were 15 bucks each at the CC dealer.