Good to replace the fluid every couple of years.
When the pump extends and retracts the jacks the fluid in the tank goes down and up. This causes air to move through the breather cap (the filler cap) and dirt, moisture, bugs what ever will get into and out of the tank. Over many cycles you may see some debris or moisture in or on the fluid.
Using a small hand pump and getting to the bottom of the tank so you can see it is great. If you start to see particles in the bottom that are attracted to a magnet you are in trouble, if just dirt then use a clean toilet brush (or large bottle brush) to scrub it down a bit and then something to wipe it out careful to not leave anything behind. No chemicals or other anything other than the recommended ATF in the tank.
Most of this is dependent on where the pump is mounted, if in a sealed compartment this is the best, however some of these are just mounted underneath everything open to all kinds of dirt. Last MH I had was like that, it was right behind the passenger front wheel and attracted all kinds of stuff had to mount a piece of a mud flap right in front of it to divert some debris. This turned into a every other year procedure for me, but yours will and may be different.
A little maintenance properly performed goes a long way.