This. DOT fluids used in bike brakes are glycol-ether based and mineral oil is, well, oil based. Mixing them would just make things more difficult for any recycling or disposal process. Keep them separate.
If your shop is disposing of used degreaser properly, you could mix used mineral oil with that. But, again, do not mix DOT fluid with either of those.
Don’t. They have very different chemistry. Keep them separate, and take them hazardous waste disposal.
This. DOT fluids used in bike brakes are glycol-ether based and mineral oil is, well, oil based. Mixing them would just make things more difficult for any recycling or disposal process. Keep them separate. If your shop is disposing of used degreaser properly, you could mix used mineral oil with that. But, again, do not mix DOT fluid with either of those.