What to do with 5 gallons of used UHF?

[sdelivery]

Yes, they make filters for cleaning and polishing used hydraulic oil, they additive package can degrade some but when used with fresh oil is fine.
I use a filter cart to double filter into a drum then I do repair work.
Pump it back in through the filter carts double filters and away we go.
Add new to make up the difference.
Mike is right about combustion residue, fuel and engine related by products.

 

[Mill Lee farm]

That said I have a issue with saving stuff I should let go. Proceed at your own peril

HA!
I think the fact that I started this thread shows I'm already a lost cause...

 

[Fasturn]

I would use it for heat treating oil harden steel. My goto is 01 and HF works just fine.

 

[Al 1]

I’ve heard tying the leg of an old pair of jeans and pouring through that works pretty good?

Make sure you take off the jeans first. Al

 

[pdentrem]

Chainsaw bar oil. One of our mechanics would grab the hydraulic oils for just this purpose.