The Indians aren’t “laundering” the rouble , for the simple reason that the laws against using the rouble DO NOT APPLY TO INDIA. India can use the rouble as they please, American and European laws have zero jurisdiction over other countries, obviously.
The Indians can buy Russian oil at any price in any quantity they choose, it’s called a free market. They can use the rouble, they can do anything they want with Russia. The West has no authority over them, as hard as that is for you to get through your thick skull.
India stronk! Russia stronk!