A complete chemical analysis of soil pore water represents a powerful diagnostic tool for the interpretation of many soil chemical phenomena relating to soil fertility, mineralogy, and environmental fate. some of the current methodologies used to extract soil pore water. In particular, four laboratory-based methods: i) high speed centrifugation-filtration, (ii) low (negative-) pressure Rhizon™ samplers, (iii) high pressure soil squeezing and (iv) equilibration of dilute soil suspensions.

A number of operational factors are: pressure applicable (i.e., pore size involved), moisture pre-requisites of the soil, pore water yielding, efficiency, duration of extraction, materials and possible contaminations for potentially toxic elements (PTE )studies.

Overview of selected soil pore water extraction methods for the determination of potentially toxic elements in contaminated soils: operational and technical aspects:http://nora.nerc.ac.uk/3943/2/Di_Bonito_et_al_final.pdf

The paper about 1975 under my researchgate with Larry Tennyson may mention a tool we used to sample and extract soil water.  It consistented on plastic pipe at various lengths, an epoxied ceramic cup on the end and a stopper with two plastic tubes, one to the bottom of the pipe and ceramic cup and one just inside of the stopper.  To push water out, we used a foot pump to pressurize the tube and force water out.  When we wanted to sample, we would evaculate (put a vacuum on) with the pump to pull water in.  When the water was in the ceramic cup, we pressurized the tube again and the pressure would push the water up the tube into the sample bottle.  When we were done, we pressurized the tube again until next time.  The approach was fairly simple and inexpensive.  We would dig a post hole to the maximum depth we wanted to sample, and then as we backfulled we used sand and when we wanted to seal off a layer, we used bentonite clay to seal off a sampling layer, added some sand for next layer, put in our next ceramic cup sampler ,more sand fill, bentonite, sand, another sampler, more sand, bentonite, etc.  I think we typically had 4-5 samplers per hole, at depths of 1/2, 1, 2, 3 and 4 feet.  The diameter of the plastic pipe was probably 1.5 to 2 inches.  I think we might have gotten the pipe, tubing and epoxy glue at hardware store and ceramic cups and stopper with two holes at Fisher Scientific.  The tubing to the bottom of the samplers may have been copper, but I think plastic.  If the water is held too tightly, you may not get a sample, but we were in the Ozarks of Missouri, and I don't remember any dry samplers, in the irrigated or control areas.  But it has been so long, and I don't remember so much on the hillslde pore water samplers.  The heavy clay may mean you might have issues pulling out water, or if water is present, it may take several hours of the vacuum working to pull water away.  Obviously if dry and the water is tightly held, you might not get much.  These are inexpensive enough, you could try out and then decide.  The pump we used was a old type hand pump sort of like a tire pump, one side was pressure, the other side vacuum as I remember. 

You could build your own suction samplers from ceramic cups of e.g. Eijkelkamp or other manufacturers and using conventional plastic pipes to glue them in, as William suggested.

My suggestion is about how to improve the sampling if it takes a long time to get the water out: We used a vacuum pump and a pressure regulator to create a constant vacuum. As a reservoir/buffer for the vacuum, we use empty beer barrels. So the pump creates a vacuum in the beer barrel. To the beer barrel you can connect several samplers: Each suction sampler is connected to a bottle. The headspace of the bottle is connected to the vacuum reservoir. So the pump will maintain a constant vacuum in the reservoir/beer barrel. This vacuum will be distributed to several bottles, to which you connect your samplers. You can switch the pump on one day and return the next day, when soil solution has been collected.