I would love to hear experiences with Asian Massage Parlors in Washington DC.  I want tp try one or two and would love some suggestions.  

Secondly, I understand you pay for the hour up front, but then you lay the "tip" on a table in plain view in the room or how does one proceed.

Thanks for any help you can give.

first, havent been to a DC MP in a couple of years. But here's how most mp's work, and the way All the ones I visited in DC work.
First, you'll find all the addresses and phone numbers in the daily Washington Post sports section. They all advertise there. M
You go in, you pay for 30 minutes or an hour. Usually $50.  Do the 30, because you are only gonna get one pop anyway, unless you want the "real" massage too. You want to add to the tip, if you want more than one pop, but you will have to spell that out to her and get her agreement in advance.

Sometimes you can ask to see the ladies that are working. So if one who you are assigned doesn't grab you, ask for a different one. Don't be shy about that. Then when you get in the room, you are asked what you want. Say "everything", look down at your vital area, or touch there. She'll understand, even if she doesn't speak english well.
Then put $100 on the table in a visible place where she WILL see it. she'll handle all the rest.
Go in with low expectations though. Expect full service, but everything covered.
The rest will take care of itself.
Just enjoy
Rick2

that pretty much sums it up

I am a huge fan of the DC locations.

Normally you can get everything you need for $120 but everything you want for 180-200.  Ask to see the girls first and you will normally be accommodated.  If they say no, leave.  You are the customer.  Mama-san will yell, but screw her.

If you are unsure, ask the girl separately for their tipping structure.  Most will be honest about what they are looking for.