don't like doing this

[Dichotomy]

I don't think he is in a tough spot at all.

There is right, and there is wrong.  The OP clearly knows what is right. 

Do the right thing. 

I believe the right thing is to refuse to break the law for your employer.

The very worse that can happen is you get fired from a place that does the wrong thing.

Then you will certainly have choices to make, many of them.

I agree.  Sad thing is I took this stance and spent two years looking for a decent job to replace the one I lost.  Actually still looking while I do something I'm not really happy at and pays sod all.

[SilverZ06]

I agree.  Sad thing is I took this stance and spent two years looking for a decent job to replace the one I lost.  Actually still looking while I do something I'm not really happy at and pays sod all.

My ethics professor told us that while whistle blowing might be the "right thing to do" you better make sure it is right for you and your career. Most times you will find yourself out of a job and possibly somewhat black listed from a particular industry. You have to think about yourself and your family that you are providing for. It almost seems better to turn a blind eye long enough to find another suitable job versus getting fired and being out of a job for an indefinite period of time.   

[WWhiskey]

When given the ability and opportunity to fix a problem yourself, ie dispose of it yourself at an oil reclamation facility, or turn it in and put yourself and maybe your family in jeopardy ,, I'd just deal with it!   But that's just me, I've always been a do'r more than the other option !

[texasmom]

I wouldn't just say "it's wrong" without bringing two workable alternatives to the same discussion.

[Dichotomy]

My ethics professor told us that while whistle blowing might be the "right thing to do" you better make sure it is right for you and your career. Most times you will find yourself out of a job and possibly somewhat black listed from a particular industry. You have to think about yourself and your family that you are providing for. It almost seems better to turn a blind eye long enough to find another suitable job versus getting fired and being out of a job for an indefinite period of time.   

I didn't think I'd do well with a potential stint in club fed.  Owners had the money for high dollar lawyers.  I didn't.

[Skyguns MKII]

I didn't think I'd do well with a potential stint in club fed.  Owners had the money for high dollar lawyers.  I didn't.

and my boss has plenty of those.

[Dichotomy]

I don't have a good answer for you Sky.  I wish I did.  I did what I felt was right and I'm still taking the hits for it.  The good news, for me, is I can hold my head up and know I did what was right. 

[Wolfala]

Take it to an airport maintenance shop. They will send you in the right disposal
Direction or take it away from you.

[DREDIOCK]

I would politely but in writing point out the error in their thinking that dumping it in a porta potty is a bad idea inasmuch as such contamination could easily be traced back to your company should the containment be discovered at the dump site which is almost surely tested by official representatives from time to time and as most porta potty companies keep records as to which unit has or is being used where. Then suggest the gas station or other solution.

Putting it in writing makes it taken more seriously. It also covers your own arse.
Whatever you do. Dont make a complaint without offering a solution. Makes you look good and not just as a whiner.