I have a 2004 Audi A4 1.8L and was wondering where the oil drain plug is located

The oil drain plug is located at the underside rear of the engine looking from the front about an inch or two from the bottom.

What color is the oil in the transmission pink or black.

all oil drain bolts are under the sump some allin key some normal bolts

Transmision oil for 2001 Audi A4 1.8 l turbo:
Manual gearbox (5 speed):
- Capacity = 2,25 liters
- Specification: Gear oil SAE 75 W 90 (synthetic oil)
Part number G 052 145 S2 (1 liter)
- To check oil level, unscrew oil filler plug placed on the left side of the gearbox in front and near of transmission axle, using an Allen 17 mm key.
- Check oil level with locally manufactured tool, e.g. a piece of angled wire.
- Specification: oil level 7 mm below bottom edge of oil filler hole.
- Install oil filler plug, tightening torque = 25 Nm.
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You must first remove the underbody engine pan to gain access to the oil pan. the plug is in the oil pan and is clearly visible.

your oil filter is under the front end you have to move engine splash shield.under the front bumper.

not sure if this link will help you out but have a look.. instructions on how to change the engine oil on 2004 Audi A4 3 0 Google...

Which plug are you refering to? Engine oil plug,transmission oil plug or radiator drain plug.

the oil filter is on the back passanger side just below the turbo the pipes from the oil cooler run into the filter housing

you have to take off the speedometer cable/wiring harness from the top of the trans and fill it from there....one 10mm bolt...very awkward spot...it might be snug, so just take a flat head screwdriver from underneath to tap it loose...