Will be just fine to use warm salt water or even plain and a bit of cotton wool to wipe out if you havent got any ear wipes before you get to the vet.

Could be ear mites but as you said more than likely infection.

One of my boys suffers from this on and off in both ears due to close ear canal flaps. I use Oticyl ear cleaner to first clean out and then a couple of drops of Canural, both from the vets and usually clears it up but if I run out occasionally I have just used water and cotton wool.