Brake levers go to the bar after sitting

I don't know if anyone else has noticed this, but it is weird. I didn't have this problem until the rainy season started. I get done riding. I park the bike and everything is working fine. 5 days later I go to load the bike to head out to the ORV park, and my brakes act like they have air in the system. The levers go to the bar when trying to stop. I eventually figured out that if I grab the calipers and push against the sliders so the pistons get pushed most of the way in, then pump up the brakes, the problem either mostly goes away, or completely goes away. But then the next time I let the bike sit, it does it again.

I have been lazy about pressure washing the bike lately, which might be related. Never had a bike that would do that though

Eh?
That's a new one.
Only thing I can think of is possibly that air contracts under cold temperatures. The reservoir has a little air sealed in there. Maybe it's creating a small vacuum?

Id pump the brakes like you have previously, then open the reservoir caps and reseal. See if it happens again?

AbnormalWrench said:

I eventually figured out that if I grab the calipers and push against the sliders so the pistons get pushed most of the way in, then pump up the brakes, the problem either mostly goes away, or completely goes away. But then the next time I let the bike sit, it does it again.

Click to expand...

What do you mean by the "sliders"? Do you mean that you make the calipers float?
Have you checked that the brake fluid levels aren't getting too low because of worn brake pads? Maybe if they get too low the brakes start sucking air into the reservoirs and when the pistons are pushed in the levels rise again. Then you use the bike, the fluid expands a little because of heat and you don't have the problem until the bike cools down.

AbnormalWrench said:

I didn't have this problem until the rainy season started.
[...]
I have been lazy about pressure washing the bike lately, which might be related. Never had a bike that would do that though

Click to expand...

AFAIK, the problem with moisture is that, when the brakes get hot, the water will start boiling and becoming vapor, which is compressible. When the brakes are cool, though, water shouldn't cause this.