Bottle brush is your only good option. I wouldn't be too concerned about it. Dowel holes and glue don't resemble the problems that could occur with typical edge to edge glueing. What is going to fail?

I have never bothered to washout bung holes in decks. Just drill them and glue them.

Likewise fancy brands of teak specific epoxy are a waste of money. Regular West System has already glued more teak than any other resin system ever will.

Addendum:

Am I correct in thinking that epoxy (and other solvent base glues - resorcinol, others....) will cut thru the oil and work just fine on Teak? That is - no need to remove the oil with solvents.

If using yellow, or other water based glue, then the oil has to removed prior to gluing with some sort of solvent.

I know I made over a hundred Teak boat doors with resorcinol in the 70's and 80's and they all stayed together very well. We never cleaned off the surfaces - just machined and glued like anything else.

Good point David; I have been using unibond 800 for all other parts of door so perhaps that is best for dowel joints?

David,

In best practice one should try to remove the oil from teak before glueing. It doesn't matter which glue. It is a contaminant.

I think of glue joints as perfect, adequate, or poor. Most of our typical pva glue joints with maple are somewhere between perfect and adequate. The gluelines may be too tight, too loose, dust may be present, surfaces may be too rough.

We spend more time prepping the most important joints. Always wipe down teak when doing bending laminates. Plugging screw holes...not so important. Dowels in doors? Just the jamming effect would almost be enough without glue. All you need is an adequate glue joint. Not perfect.

I've only seen a few epoxy teak joints fail where I concluded it was the oil(that was not removed). However, it could have been for other reasons.

Unless you are involved in boatbuilding one would be completely unaware what has been done with epoxy and teak. For instance many, many sailboats up to 50' in length have had fake teak decks applied. The west system boys invented it along time ago in a galaxy far far away. They rip 2" teak planks into 1/4" strips and bond them directly to a plywood deck with nothing but epoxy thickened with graphite powder. These are screwed and plugged.

On the boats longer than 50' they glue up templated panels off the boat and then vacuum bag them down in huge sections with just epoxy. No screws required.

I have mentioned 100 times on Woodweb that the majority of epoxy failures are from smooth surfaces and tight joints. This is simply avoided by abrading every part with 80 grit paper. It creates a proper width glue joint and provides surface area. It is mentioned in every epoxy manual. Abrade the metal, fiberglass, and wood with 80 grit. My rant has concluded.

David, Epoxies aren't solvent adhesives, and most aren't particularly good on oily woods as the oils stop penetration.
Adhesives carrying solvents that are capable of dissolving the oils in question will of course be carried into the grain by the solvents. Adhesives that are not oil friendly will require a degreasing prior to use, the acetone and bottle brush or other mechanisms.
I do fully accept that the gluing of a peg into a hole is a relatively fascile task, requiring little of an adhesive, as Adam suggests, but the performance of specialist glues for specialist areas is vastly different. All the epoxy manufacturers make different resins for different jobs, and a comparison of an uncleaned end grain join between a specialist oily wood epoxy and a non specialist one will show major differences.
Never hurts to use an appropriate tool though, in this case, many tools will suffice.

A sufficiency.....

Am I imagining this or is the plantation teak today far less oily than old growth Burma teak?