A transponder code (0034) has been approved for use for sailplane towing. Any transponder equipped aircraft conducting towing operations can use it in the course of towing, including descending after the tow, etc.
If crossing controlled airspace while towing (eg class D or E), a pilot may be asked to squawk a different code for identification. We suggest pilots use 7000 if on transit to a retrieve in class G.
Any club that has a pre-existing agreement on transponder codes with a local air traffic unit should discuss the situation before changing the code used.
Details are listed in the AIP under ENR 1.6 ATS Surveillance Services and Procedures.