Thank You all for the valuable comments, and into. Just to better explain my setup. It's a Tank (88cm x50cm sized, 15cm DEEP) used as a foot bath. So the idea is to regulate the heat using 1-2 heaters to maintain it constantly between 25-35 C. (no need to be exactly 25 or 30 at this stage). At this stage the contents of the tank will be pure water...so I dont think I have to consider pressure as a significant factor on the sensor. yet it will be constantly "underwater". The tank is made from 15mm thick acrylic sheets.
As suggested, I think http://arduino-direct.com/sunshop/index.php?l=product_detail&p=151 or http://shop.boxtec.ch/product_info.php/cPath/39_71/products_id/40326 seems to be a good choice.
Thanks again all for the helpful comments. For your information I also found a similar project which had my requirements, although the probe was a DIY sealing.
http://makeprojects.com/Project/Yobot-Arduino-Yogurt-Maker/499/1