Take a look at Lomo drybags. Really robust roll tops and a fraction of the price of a 'bike specific' version. They come in loads of sizes up to about 100 litres, though the 80 litre version took all my gear including the tent and cooking stuff. Highly recommended.
@chizel, Noobie's hacked your Flickr account and nicked your old school photos. You need to change your password mate.
I'm surprised how much clothing people take, even the light travellers. Five changes of underwear is sufficient for me. I can always manage to get washed and dried to ensure a fresh set each day. I take one set of off-bike evening wear and all my clothing (everything I take in fact) will be as low bulk, light weight as possible. Not an ounce is wated in my luggage. Nothing, not a scrap of packaging that isn't absolutely necessary gets through the selection process. All my off-the-bike clothing will be gear I wouldn't normally wear at home. Shirts, trousers, socks, will be quailty low-bulk, light weight stuff designed for back packers. Low-odour, quick-drying and very comfortable to wear. I'd never take take heavy things like jeans. Towels will be micro towels, even my toiletries will be traveller-sized items in a back-packer toiletry bag. I like to be clean and comfortable off the bike but you don't need to be weighed down on it to achieve that. I once spent a year travelling round Australia in an old station wagon with the former Mrs Gimlet who was a women who worked in the fashion industry and thought it not unreasonable to be fined £150 excess baggage at Heathrow purely to transport sleeveless tops and a vast collection of underwear to the other side of the world. Many things were learned on that trip.. I'll typically take one pair of light weight trousers, one long sleeved shirt, a spare mid-layer T-shirt for riding (the other I'll be wearing), a light jacket or or low-bulk warm fleece. When I go to Scotland this June I'll take some light waterproof walking boots and a decent waterproof jacket and trousers. I'm not going to Scotland and missing the chance to strike out on my own two feet now and again, especially if the weather is wet. I'm even taking (decent quality again) a travelling fishing rod because the river Moriston runs right behind the cottage and guests have free fishing rights. It would be criminal not to. All my clothing and toiletries will go into a 30L Kriega tailpack. If I'm camping with a three-man tent (you need at least double the size you think you'll need on a bike with all the luggage and riding gear), cooking gear, folding chairs, beds and bedding and all the paraphernalia, I'll still only take the kriega back-pack for personals and the 40L dry bag for all camping gear and bike spares/stuff etc. With the two 20L Enduristan roll bags I've just bought which I'm using as panniers, I expect the KTM 40L bag will be too big. I do have a smallish quick-release tank bag for valuables/essentials/change etc. It usually suffices as a day-bag.
On my annual Euro scooter trip in 2016, I ran out of T-Shirts, so I overdid it last year. I wore about a 1/3 of what I took. I had the piss taken out of me mercilessly. Check out the mule for a 5 day trip.
By the very nature of washing your socks and pants are clean alternatively you could cart 20 pairs of dirty pants and socks around in the latter part of your trip .....your room awaits in that case
Touche !! But.... I just take a bin bag for dirty laundry, so that I don't have to be Dot Cotten on my holiday and start washing pants in the sink you pikey !!
If you take clothing that's designed to be hand-washed in a sink and drip-dried and you use a specific hand-washing laundry liquid (in a handy travel size), there is no problem. (I wash mine in a sink - or collapsible bowl if camping - and to rinse them out I take them in the shower). If you're taking heavy denim jeans and a 2 kilo box of Bold 2 in 1 that could be where you're going wrong.