When I go to drain the black water tank the slide out device is very hard to pull out. I have used two types of lubricants on it to help "it slide" but to no avail. Any suggestions, the waste water ...
Possibly something stuck in the slide valve seal. If your valves are cable operated then you should to check the cable for kinks or corrosion. If it's a real problem I think the valves are less than $20 so it might be easiest to just swap it out. Assuming your tank is empty.
Also, you might want to check the screws in each corner of the valve. If they are too tight they tend to squeeze the blade and make operation difficult.