Where is the hydro unit filler tube?

check for a blocked air breather for the sump

Not to panic... the oil should burn off. It will just be a little embarrassing to have all that smell and white smoke until it does! However, the real question is, how did oil get on the spark plugs in the first place? If you spilled some oil on it, don't worry. If you left the oil filler open, make sure you check your oil level and close it. If you overfilled the oil level in your mower, drain some of the oil out.

Remove oil filler cap which is normally on top of the rocker cover look at underside of cap, the side that goes into rocker cover, and if it is covererd in a white oily substance or if the tube that the filler cap goes into has the white gunge in it yo have oil and water / coolant mixing in your engine

bad hdro pump but first try and change hydro oil and filter sometimes it works

If it isn't on the bottom of the engine (above the blade) then you don't have one. This is not that uncommon. When you need to drain the oil, FIRST- pull the spark plug wire off!!! Then remove the dip stick or filler plug and turn the unit upside down and drain the oil.

could be the head gasket have a look in coolant expansion tank for signs of oil,undo oil filler cap and look at underside of cap if have a white sludge indicates water in oil ,are you having to refill the coolant regulerly ?if nothing noticed have a hydro-carbons test done at local garage take it from there ,let me know how you get on

https://www.manualslib.com/download/809988/White-Outdoor-Lt-1650.html Better late than never.

The drain plug on a Briggs and Stratton engine is underneath the deck. Most likely it is concealed by cover for the self propel belt and possibly the blade as well.
The suggested method for draining the oil is to warm up the engine by running the unit for 10 minutes or more, though this should be sufficient time for the engine to have warmed up. Then drain the oil.
An alternate method is to drain the oil out of the oil filler tube. To do this, after the engine is warmed up, tilt the mower onto the side that has the oil filler tube. Put the drain pan under the filler tube, then remove the filler cap. The oil will drain out into the oil drain pan.
CAUTION: The oil that will come out of the engine will be HOT! So be careful when removing the oil filler cap.
I hope this will answer your question. Best of luck in this mowing season.

I haven't looked at a 09 model but earlier models used a 7/16 inch allen key.