This is the crankcase drain plug just to the right of the engine oil filter housing. This should be removed to drain oil and clean the magnet in accordance with Aprilia engine service intervals of 7,500Km (4,650 miles)
Original Aprilia Part (01-07) No: AP0241782 later revised to 2R000498
Optional crush washer used by Aprilia 07-10 and OK to retrofit to our bikes: AP0250640
Alternative magnetic plug from KTM: 58030021100 – Fowlers UK (May 2020)