Budget Travel Around Europe using EUROLINES PASS: Your Guide to a Pleasant Bus Journey

Once you have purchased your Pass online, make sure you print it before leaving home. 

Book your first journey at least a day ahead of your scheduled travel. Eurolines stations usually has one window for sales/booking, and two windows for check-in. 

Get your ticket from the Sales window. They shall print out your ticket for the journey.

I remember somewhere in the fine print, they say that you may be charged for a "reservation fee". Of all the eight countries I visited, only Germany and Vienna charged around 5 euros per ticket.

On the day of your journey, you have to be at the station at least an hour before the bus departs (although they can be quite flexible with this. When I left Brussels for Amsterdam, the bus was scheduled to depart by 6am, but I got there 5:45am. They still took me in).

Upon check-in, they will give you a baggage tag, and a boarding pass. Each country varies. Some print it on paper, others are printed on a plastic card.

If your journey has several destinations, they generally have separate compartments per destination. e.g. the baggages go to the right side of the bus if your destination is Brussels, and they go to the left if you're bound for Amsterdam.

After putting your baggages inside,  you queue again to board the bus. You hand the driver your boarding pass and just sit anywhere you fancy.

All buses have built-in toilets, located typically at the middle of the bus. Door handles/knobs vary but you just have to twist it to open. In our trip from Brussels to Amsterdam, I must have twisted the knob several times until I gave up and went to the driver. Apparently, it was locked so he had to give me the key to open it.

Flush, most of the time, has a button by the bottom of the sink which you can push easily with your knees. Otherwise, there's a rubbery button at the back of the toilet seat which you just press. 

top button : to activate water to wash your hands
bottom button : to flush
BUT.. you already know that ;)

buttons conveniently located below the sink so you can push it with your knee

Depending on the journey, there are trips that take a rest stop at a gas station/ convenience store (Paris - Brussels); others just go straight ahead through the journey and stop along the destinations (Brussels - Antwerp - Rotterdam - Den Haag - Amsterdam).