mix acrylic with lysol.
No one knows about this, but lysol melts the shit out of paint, and if used correctly, can thin most film/water based paints. It sounds weird, but give it a try.
For added stain-i-ness, throw in some pen ink and/or fiebings. Lysol really mixes with everything, so you can make a pretty good indoor/outdoor ink. Also, if you mix pen ink with acrylic, t has a tendency to stay on the bottom, so when you catch a tag, it'll stain hard even if you clean off the acryl part of the tag.