Wondering if you had a steam cleaner is that would also work?

After steam cleaning, will you polish the inside of the pipe/manifold for even better flow?

and maybe some flow porting.

I heard Juice polish is the best...
Consider that some racers finish their race with many dents on their pipes without any real drop in real world performance: time to focus on other improvements like reduced rotational mass, two belt systems, etc....

There are also solutions to prevent burn in dirt on the pipe. Many people here use a high temp vaseline and some RC brands have a spray can with some exhaust protection liquid with which afterwards it is easy to wipe off the dirt.

Antifreeze in a crockpot is by far the best method. Not sure what you're so worried about. Set it up in your basement or on a porch/stoop/balcony. Antifreeze isn't going to hurt anyone if you aren't drinking it.

Did OP try any of the solutions or methods being posted? I am curious how it turned out.

I haven't tried it yet, but I will soon and will update you on what turned out to be better. The main thing I'm looking for is to clean the inside, which is the most important thing for me.

Ya let us know the results. If possible it would be interesting to see before + after pictures.

Paint stripper that contains dichloromethane is the best.

Put it in a glass jar with a airtight lid overnight, rinse with water 100% clean inside and out. Not 99% clean, 100% clean.

I’ve heard of folks doing this at some point.